This invention relates to a method for preparing cyclic oligomeric polycarbonates from dihydric phenols and carbonyl halides, and more specifically, a method of preparing cyclic oligomeric polycarbonates from the water soluble metal salts of dihydric phenols and carbonyl halides by interfacial polymerization.
Polycarbonates are typically produced by the reaction of dihydric phenols such as, bisphenol, with a carbonyl halide such as, phosgene, by an interfacial reaction using a mixed aqueous/organic system which results in the recovery of the carbonate in the organic phase. Low molecular weight cyclic aromatic carbonate polymers and their preparation are described in U.S. Pat. Nos. 3,155,683, 3,274,214 and 3,422,119. The cyclic polymers disclosed therein are single compounds. In U.S. Pat. No. 3,155,683, the cyclic aromatic carbonates are prepared by reacting together in an inert organic solvent containing an acid acceptor and as the sole reactive ingredients, water and a specified class of bishaloformate. A typical acid acceptor is pyridine, and the bishaloformates are typically bischloroformates derived from 2,2Bis-(4-hydroxyphenyl) propane. The acid acceptor in U.S. Pat. No. 3,155,683 is typically a tertiary amine, such as triethylamine, or an alkali metal oxide or hydroxide or an alkaline earth metal oxide or hydroxide. Cyclic polycarbonate oligomers are also prepared from bischloroformates as described in U.S. Pat. No. 4,616,077. The preparation of cyclic polycarbonate oligomer mixtures is described in U.S. Pat. No. 4,644,053, the disclosure of which is incorporated herein by reference. In that patent, the preparation of the mixtures is typically by the reaction of a corresponding bischloroformate composition with an alkali metal hydroxide and a tertiary amine.
In U.S. Pat. No. 3,274,214, cyclic aromatic dimers and trimers are prepared by contacting, in the presence of an acid acceptor, a specified class of dihydric phenol with a carbonyl halide to provide a reaction mixture containing the cyclic carbonate polymer. In U.S. Pat. No. 3,422,119, a cyclic carbonate dimer is prepared by reacting in the presence of an acid acceptor, a dihydric phenol of specified formula with a bishaloformate of a dihydric phenol of a specified formula.
When an ortho-bisphenol is reacted with a carbonyl halide in the presence of an acid acceptor which is essentially a weak base of the order of basicity of a tertiary amine, a cyclic carbonate monomer is produced, but if the reaction of a carbonyl halide with an orthobisphenol is carried out in the presence of an acid acceptor which is a strong base, such as sodium hydroxide, the resultant product is the expected linear carbonate polymer as disclosed in U.S. Pat. No. 3,221,025. However, in U.S. Pat. No. 3,221,025, when a carbonyl halide reacts with a bisphenol, other than an ortho-bisphenol, such as a para- or a meta-bisphenol, in the presence of a weak base such as a tertiary amine, linear carbonate polymers are formed. Other cyclic carbonates, such as cyclic carbonate trimer, are prepared by methods as discussed in U.S. Pat. Nos. 4,129,574, 4,139,687 and 4,197,394.
In U.S. Pat. No. 4,368,315, there is described a catalyzed equilibrated interfacial polycondensation aromatic polycarbonate process wherein an equilibrated, substantially uniform agitated two-phase admixture containing an organic phase with inert solvent and an aqueous phase with a solution of an aromatic dihydroxy compound and a strong base, is formed, and a carbonyl halide is added thereto and reacted with the aromatic dihydroxy compound to form an aromatic polycarbonate. In U.S. Pat. No. 4,368,315, substantially all of the polycarbonate formed during the reaction precipitates in-situ in the aqueous phase in particulate form. In the critical process sequence of U.S. Pat. No. 4,368,315, an equilibrated, substantially uniform agitated two-phase admixture is formed and contains an organic phase containing inert solvent and a polycondensation catalyst and an aqueous phase containing a solution of an aromatic dihydroxy compound, and a strong base having a pH of at least about 11, subject to the proviso that the volume ratio of inert organic solvent phase to aqueous phase is within the range of from 0.04:1 to 0.20:1, and the mole ratio of the base to aromatic dihydroxy compound is at least about 0.25:1. The carbonyl halide is added to and reacted with the aromatic dihydroxy compound to form an aromatic polycarbonate having a molecular weight of at least about 2,000. The solid aromatic polycarbonate particulate is separated and recovered from the liquid aqueous phase. The polycarbonates prepared by the process of U.S. Pat. No. 4,368,315 are preferably non-sterically-hindered aromatic polycarbonates.
Many of the foregoing processes are multi-step processes and are disadvantageous because of the excessive amounts of carbonyl halide, such as phosgene, required to carry out and complete the reaction. In those processes where cyclic oligomeric polycarbonates are prepared by the hydrolysis of bischloroformates and equivalent reactions, half of the chloroformates are lost to hydrolysis, thereby leading to insufficient utilization of the carbonyl halide. Furthermore, in many of the prior art processes, an excessive amount of the linear polycarbonates are formed along with the cyclic polycarbonates and/or high polymer products are formed along with the desired low polymer products during the reaction.